In the search for lesions in the large intestine or other regions of the intestine, volume data records from slice image methods, such as computed tomography or magnetic resonance imaging, are utilized. In this case, a volume data record is understood to be a 3D image data record. During the tomographic imaging, the intestine is filled with a suitable contrast agent and can be segmented from the data record. Subsequently it is visualized for the user by means of a suitable visualization technique, for example by using multiplanar reformatting (MPR) or by way of a virtual flight.
However, in the clinical routine, the intestine is often not filled completely with the contrast agent during the image recording. The sections of the intestine which are not filled are collapsed and cannot be examined. If a lesion is located there, it is not recognized during the recording and displaying of only one image data record. This problem is generally avoided by recording two tomographic volume data records in two different positions of the patient, usually in the prone and dorsal positions. Here the assumption is made that the contrast agent is differently distributed when the patient is repositioned, different intestinal sections are contrasted or collapsed, and 100% of the intestinal surface is visible and can be examined when observed over both data records.
During this procedure, the user is required to be able to navigate from a particular position in the image of the intestine of the one patient position to the identical position in the image of the other patient position. This requires that the two image or volume data records are registered. Using the registration matrix generated during the registration, the corresponding image voxel in the other volume data record can then be found for every image voxel in the one volume data record.
Recording the tomographic volume data records in different positions of the patient is also advantageous in that residual stool remaining in the intestine can be distinguished from possible lesions. Despite patient preparation using medication, such residual stool stays in the intestine and can lead to an erroneous diagnosis if only one volume data record is used. Residual stool does not adhere to the intestinal wall in most cases but follows the gravitational pull and therefore always lies on the bottom side of the intestinal tube in any patient position. It is for this reason that in the case of suspicious structures in one patient position, the corresponding position in the other patient position is always examined in the respective volume data records. If the structure of interest follows the gravitational pull when the patient is repositioned, it does not adhere to the intestinal wall and therefore the possibility of a lesion can be ruled out. The registration of the two volume data records in this case also permits quick comparison of the identical position in the intestine in the two volume data records.
Until now, such volume data records of the intestine have been registered on the basis of so-called central lines. These central lines can be middle lines of the segmented intestine, lines according to the “longest view” method or flight paths in the intestine generated automatically or by the user. In any case these central lines follow the profile of the intestine in the respective image data records. Then similarities are determined between the central lines of the image data records to be registered, in particular of the prone and dorsal positions of the patient, and are used to calculate the registration matrix. However, for many regions of the intestine the registration matrix determined in this manner is only imprecise. This is because the intestine only has three fixed points in the body but can otherwise, particularly after the repositioning, be at different positions in the abdominal cavity. When navigating in the image data records on the basis of such a registration matrix it is therefore only possible to navigate in each case to the vicinity of the desired position when switching from one image data record to the other.